1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer and to a developing apparatus for a use in these apparatuses.
2. Discussion of the Background
Conventionally, as a developing apparatus for developing with two-component developer including toner and carrier, there is known a developing apparatus in which toner is taken into developer according to behaviors of the developer without a need for a toner density detecting device.
In such a developing apparatus, however, a toner feeding amount depends upon whether or not a behavior of the developer is active and whether or not the developer is abundant in respective places, thereby partially causing the toner density to be unstable, which easily results in fogging or an uneven image density.
Accordingly, in Japanese Patent Application No. 63-4282, for example, to prevent fogging or an uneven density on an image as described above, there is proposed a developing apparatus having two toner supplying regulating members as described below. A first toner supplying regulating member has a fixed end above a doctor blade, which is a developer regulating member for regulating a developer layer thickness on a developer bearing member. The first toner supplying regulating member extends toward a toner supplying tank which is a toner container section. A second toner supplying regulating member is arranged closer to the toner supplying tank than the first toner supplying regulating member. The second toner supplying regulating member extends from the upper portion of the developing apparatus downward, partitioning the developing apparatus into a developer container and a toner supplying tank. The lower free end of the second toner supplying regulating member is on an extension line of a free end of the first toner supplying regulating member or in the developer bearing member side.
In the above developing apparatus, a portion of the uppermost developer layer on the developer bearing member, where developer is relatively coarse and thereby toner is easily taken into, moves to a regulating position of the above doctor blade in a condition of a higher toner density than that of the developer layer on the developing bearing member in the vicinity of the surface of the developer bearing member. Such a movement of the portion of the uppermost developer layer on the developing bearing member, however, is prevented at the free end of the second toner supplying regulating member before the developer layer enters into the developer layer thickness regulating area enclosed by the first toner supplying regulating member, the developer bearing member surface, and the doctor blade. This prevents developer of an extremely high toner density from being supplied to the developer layer thickness regulating area, and only toner sufficiently charged by a friction with magnetic particles is conveyed to the developing area opposite to the image bearing member, such that a fogged strip (background soiling) on an image and an uneven image density in a direction perpendicular to a developer conveying direction with the developer bearing member or the like are prevented.
A developing apparatus previously proposed by the applicant of the present invention and disclosed in Japanese Patent Laid-open Publication No. 9-197833 is useful for dissolving the above-described disadvantages while achieving down-sizing and a lower cost of the apparatus.
The developing apparatus in Japanese Patent Laid-open Publication No. 9-197833 internally has a magnetic field generating device, a developer bearing member for bearing and conveying two-component developer including toner and magnetic carrier, a first regulating member for regulating an amount of developer born and conveyed by the developer bearing member, a developer container section for containing developer scraped off by the first regulating member, and a toner container section arranged adjacent to the developer container section for supplying toner to the developer bearing member. The developing apparatus changes a toner take-in condition of the developer on the developer bearing member by changing a contact condition between the developer and the toner according to a change of the toner density of the developer on the developer bearing member. The developer container section has a second regulating member arranged upstream of the first regulating member in the conveying direction of the developer on the developer bearing member, and the second regulating member is spaced from the developer bearing member so as to regulate a passage of an increase of the developer when the developer layer thickness is increased due to a rise of the toner density of the developer on the developer bearing member. According to this developing apparatus, the toner and the magnetic carrier in the developer are agitated by a cyclic motion of the developer in the developer container section so as to prevent a charged amount of the toner from being reduced, thereby avoiding an occurrence of an abnormal image such as an image having an uneven image density or fogging while achieving down-sizing and a lower cost of the apparatus by reducing the number of components.
FIG. 1 illustrates an example of a developing apparatus related to the above Japanese Patent Laid-open Publication No. 9-197833, and FIG. 2 is an enlarged view of a main portion of the developing apparatus for assistance in explaining behaviors of the developer in the developing apparatus. The developing apparatus includes a developing sleeve 1 as a developer bearing member containing a permanent magnet as a magnetic field generating device, a first regulating member 2 for regulating a layer thickness of developer 22, a developer containing case 4 as a developer containing member for forming a developer container section 3 for containing developer which is obstructed by the first regulating member 2 upstream of the first regulating member 2 in a rotary direction of the developer bearing member, and a toner hopper 6 arranged adjacent to the developer containing case 4 for containing toner. The toner hopper 6 is in communication with the developer container section 3 through a toner supplying path 7 as a toner supplying aperture. Inside the toner hopper 6, there is provided an agitator 8 as a toner agitating member for conveying stored toner 5 to the toner supplying path 7 while agitating the toner 5. Furthermore, at the lower end of the developer containing case 4, there is provided a second regulating member 9 spaced from the developing sleeve 1 so as to regulate a passage of an increase of the developer 22 when a layer thickness of the developer 22 is increased due to a rise of the toner density of the developer 22 on the developing sleeve 1.
In the developing apparatus illustrated in FIGS. 1 and 2, when a toner density of the developer 22 passing the first regulating member 2 is within a predetermined appropriate range, the developer 22 scraped off by the second regulating member 9 forms a developer stagnated portion 10. Then, the developer stagnated portion 10 clogs the toner supplying path 7, and taking-in of toner 5 from the toner hopper 6 into the developer containing section 3 is stopped in this condition. In the developer stagnated portion 10, the developer 22 scraped off by the second regulating member 9 is received by a toner supplying stage 14b, which is provided integrally with a developing apparatus frame 14. The toner supplying stage 14b is inclined downward to the developing sleeve 1 and has a predetermined length, thereby the developer 22 is prevented from dropping to the toner hopper 6 by a motion of the layer of the developer 22. Accordingly, a constant amount of the developer 22 can always be maintained on the developer sleeve 1 and a self-regulation for constantly supplying toner to the developer 22 is achieved. When a toner density of the developer in the developer container section 3 is decreased by a toner consumption, developer is taken into the developer container portion 3 from the developer stagnated portion 10. Then, a volume of the developer forming the developer stagnated portion 10 is decreased, by which the toner 5 is started to be taken-in again into the developer 22 and is continued to be taken-in until the toner density of the developer 22 reaches a predetermined density.
In the developing apparatuses proposed in Japanese Patent Application No. 63-4282 and Japanese Patent Laid-open Publication No. 9-197833, the layer thickness of the developer on the developer bearing member in an axial direction of the developer bearing member is regulated by a blade-like member as the second toner supplying regulating member or the second toner regulating member (hereinafter referred to as xe2x80x9csecond regulating memberxe2x80x9d), which is arranged to face the developer bearing member. Because the above second regulating member has just a small facing area to the developer bearing member, if a gap between the second regulating member and the developer bearing member is uneven in the axial direction of the developer bearing member due to a processing precision of the facing surface, it is very likely that a developer layer is formed with an uneven thickness. Further, unevenness of the developer layer thickness leads to an uneven amount of toner taken into the developer, thereby sometimes causing an uneven image density in the axial direction of the developer bearing member.
To solve the above-described problem, it is conceivable to increase a processing precision of the facing surface of the second regulating member, but it leads to an increase of cost of the apparatus.
In the developing apparatus proposed in Japanese Patent Laid-open Publication No. 9-197833, there is a disadvantage of causing an uneven image density due to insufficiently charged toner which locally exists. Referring to FIG. 2, the toner 5 is conveyed to the developer container section 3 passing through a path as indicated by an arrow in the drawing when the toner density of the developer 22 is lower than the appropriate range. The toner 5 is charged to some extent by friction with the developer 22 when passing a contact interface between the developer stagnated portion 10 and a developer layer on the developing sleeve 1. At this time, the charged amount for the toner 5 is almost proportional to a magnitude of a frictional force between the developer stagnated portion 10 and the developer layer on the developing sleeve 1. Therefore, to achieve a sufficient charged amount for the toner 5, this frictional force needs to be enough. The magnitude of the frictional force is proportional to a conveying force of the developer 22, in other words, to a magnitude of a normal component of a magnetic force applied to the developer 22 by the magnetic field generating device inside the developing sleeve 1.
The frictional force caused by the magnetic force is not enough to charge all of the toner 5 taken into the developer 22 by a sufficient amount, and therefore there locally remains insufficiently charged toner 5. Accordingly, if the insufficiently charged toner 5 flows into the developer container section 3 and is conveyed to the developing area, an inferior image having, for example an uneven density, is generated due to partially different consumed toner amounts when printing an image requiring a large amount of toner, such as a halftone image.
Further, in the above developing apparatus, toner is sometimes directly put in contact with developer being conveyed by the developer bearing member. If the toner is directly put in contact with the developer and thereby the developer having a relatively high toner density enters the developer container section, the toner density of the developer cannot be sufficiently made uniform only by a cyclic motion in the developer container section. Accordingly, an uneven toner density may occur, thereby causing an uneven image density.
Therefore, in Japanese Patent Application No. 10-50185, the applicant of the present invention proposed to further include a developer circulation forming device for forming a developer circulating portion where developer which has been obstructed by the second regulating member is circulated upstream of the second regulating member in the developer conveying direction, and a developer stagnated portion forming device for forming a developer stagnated portion where developer stands still, when the developer toner density is within a predetermined appropriate range, in a toner supplying path connecting the above toner container section with the developer circulating portion.
In this Japanese Patent Application, there is disclosed a developing apparatus illustrated in FIG. 3 as an embodiment of the invention. The developing apparatus illustrated in FIG. 3 is characterized by having constructions described below in addition to the construction of the prior application illustrated in FIG. 1. That is, a toner supplying path 7 is configured to form a developer stagnated portion 10 with a portion of a developer containing case 4 where the second regulating member 9 is formed and a partition 12 arranged so as to face the developer containing case 4, so that developer in the toner supplying path 7 is stagnated in the developer stagnated portion 10 when the toner density of the developer is within an appropriate range. In downstream of the developer stagnated portion 10 in the toner supplying path 7, there is formed a developer circulating portion 11 having a size of causing a cyclic motion of developer by the second regulating member 9 and the developing apparatus frame 14, which is formed integrally with the toner hopper 6 so as to enclose a lower portion of the developing sleeve 1.
In the above developing apparatus, there is formed the above-described developer circulating portion upstream of the second regulating member in the developer conveying direction. Further, the apparatus is configured such that, when the toner density of the developer is within a predetermined appropriate range, toner is prevented from being taken into developer at a contact portion between the toner and the developer in the developer stagnated portion where developer stands still. When the toner density of the developer is decreased, the developer stagnated portion disappears by being taken into the developer circulating portion due to a decrease of a volume of the developer. As a result, the developer is put in contact with toner in the developer circulating portion and the toner is mixed with the developer by agitation in the developer circulating portion before the toner is taken into the developer on the developer bearing member.
In this manner, when the toner density of the developer is appropriate, a developer stagnated portion is formed, which then prevents toner from being directly put in contact with the developer conveyed by the developer bearing member. When the toner density of the developer on the developer bearing member is decreased after the toner has been consumed, developer having a high density, in which toner has been previously mixed in the developer circulating portion, is put in contact with the developer carried on the developer bearing member and having a low density, by which the toner is supplied to the developer and relatively even toner replenishment is achieved.
In the developing apparatus illustrated in FIG. 3, however, a developer bridge is sometimes formed between wall surfaces in the toner supplying path 7, in other words, between the developer containing case 4 and the partition 12, by the developer stagnated in the developer stagnated portion 10 in the toner supplying path 7. By this bridge of the stagnant developer, supplying of toner from the toner hopper 6 is stopped and a space is formed in a lower portion of the developer stagnated portion 10, even when a volume of developer is decreased in the lower portion of the developer stagnated portion 10. Therefore, there is a possibility of causing the toner density to be unstable.
Accordingly, in the above Japanese Patent Application, there is also proposed a developing apparatus in which at least one wall surface forming the developer stagnated portion in the toner supplying path includes a moving member which is moved by an operation of the developing apparatus. This developing apparatus is capable of breaking the bridge of the stagnant developer stagnated between the wall surfaces around the developer stagnated portion in the toner supplying path by a motion of the moving member.
In the developing apparatus proposed in the above Japanese Patent Application, however, sometimes the effect of breaking the bridge of the stagnant developer is not enough. Therefore, it is desirable to achieve a developing apparatus which allows a relatively even toner replenishment without arranging the above partition 12.
It has been found, however, that if the partition 12 is removed from a portion between the toner supplying path 7 and the toner hopper 6 in the developing apparatus illustrated in FIG. 9, there is a possibility that developer in the developer circulating portion 11 overflows into the toner hopper 6 at agitation for mixing the developer in the developer circulating portion 11 with toner in the toner supplying path 7 put in contact with the developer. This overflow occurs when the toner density of the developer is decreased and the developer stagnated portion 10 is taken into the developer circulating portion 11 and thereby the developer circulating portion 11 extends toward the toner hopper 6 in the toner supplying path 7. That is, developer in a portion of the developer circulating portion 11 distant from the developing sleeve 1 diffuses due to a weak binding force of a magnetic force applied by the developing sleeve 1 and thereby overflows into the toner hopper 6 from the toner supplying path 7. If the developer overflows into the toner hopper 6, a magnetic carrier amount of the developer born by the developing sleeve 1 is reduced, by which the toner density fluctuates.
In the developing apparatus illustrated in FIG. 3, when the toner density of developer on the developing sleeve 1 is decreased, the developer in the developer circulating portion 11 is put in contact with the toner 5 in the toner supplying path 7 and the toner 5 is mixed with the developer by agitation in the developer circulating portion 11. The toner 5 thus agitated and mixed with the developer is circulated by a cyclic motion of the developer circulating portion 11 and taken into the developer on the developing sleeve 1 at the contact portion between the developer layer on the developing sleeve 1 and the developer circulating portion 11. If the developer on the developing sleeve 1 has an ear crack portion (a gap between developer ears) at this point, the toner 5 is actively taken into the ear crack portion of the developer. It is assumed that this is because there are a lot of air gaps in the developer having an ear crack portion in comparison with a portion of the developer where the developer is close together and the developer does not have any ear crack portions, and the toner 5 is taken into the air gaps.
In the developing apparatus in FIG. 3, however, an ear crack portion of the developer, which is formed in the toner supplying path 7 by a magnetic pole opposite to the developer circulating portion 11, collides with the developing frame 14, by which the ear crack portion is disturbed. Therefore, the developer born by the developing sleeve 1 by the magnetic pole and in contact with the developer circulating portion 11 cannot form a stable ear crack portion. Accordingly, there is a possibility that the toner cannot be actively taken into the developer, and thereby the toner is not sufficiently taken into the developer in some portions. This unevenness in taking in toner causes an uneven toner density, by which there is a possibility of causing an uneven image density in forming a halftone image.
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Preferred embodiments of the present invention provide a developing apparatus and an image forming apparatus using the developing apparatus, in which toner is taken into developer on a developer bearing member according to a motion of the developer without a need for a toner density detecting device and in which it is possible to prevent an occurrence of an uneven image density by keeping an even toner take-in amount in an axial direction of the developer bearing member.
The preferred embodiments further provide a developing apparatus and an image forming apparatus using the developing apparatus, in which toner is taken into developer on a developer bearing member according to a motion of the developer without a need for a toner density detecting device and in which it is possible to prevent an occurrence of an uneven image density caused by an insufficiently charged toner.
The preferred embodiments further provide a developing apparatus and an image forming apparatus using the same developing apparatus, in which toner is taken into developer on a developer bearing member according to a motion of the developer without a need for a toner density detecting device and in which it is possible to prevent a developer bridge from being formed by stagnant developer and developer from overflowing into a toner container section so as to stabilize a toner density and to achieve a more stable and even image density.
The preferred embodiments further provide a developing apparatus and an image forming apparatus using the same developing apparatus, in which toner is taken into developer on a developer bearing member according to a motion of the developer without a need for a toner density detecting device and in which it is possible to form a stable ear crack portion of developer so as to stabilize a toner density and to achieve a more stable and even image density.
According to a preferred embodiment of the present invention, a developing apparatus includes a developer bearing member having a magnetic field generating device internally and configured to bear and convey two-component developer including toner and magnetic carrier, a first regulating member configured to regulate an amount of the developer born and conveyed by the developer bearing member, a developer container section for storing the developer scraped off by the first regulating member, a second regulating member arranged upstream of the first regulating member in a conveying direction of the developer on the developer bearing member, and a toner container section for supplying toner to the developer bearing member. The developing apparatus changes a toner take-in condition of the developer on the developer bearing member by changing a contact condition between the developer and the toner according to a change of a toner density of the developer on the developer bearing member. A surface of the second regulating member facing the developer bearing member has an area large enough to unify a layer thickness of the developer on the image bearing member in the axial direction of the developer bearing member.
Because of the surface of the second regulating member facing the developer bearing member having an area large enough to unify the layer thickness of the developer in the axial direction of the developer bearing member, even if a gap between the second regulating member and the developer bearing member is uneven in the axial direction of the developer bearing member due to a processing precision of the facing surface, the unevenness of the layer thickness is eliminated by superimposition during a passage of the developer through the facing surface of the second regulating member and thereby an averaged layer thickness of the developer is achieved. The averaged layer thickness of the developer makes it possible to achieve an even toner take-in amount in the axial direction of the developer bearing member, thereby preventing an occurrence of an uneven image density.
According to another preferred embodiment of the present invention, in the above developing apparatus, the developer container section is formed downstream of the second regulating member in the developer conveying direction, and the facing surface of the second regulating member is extended toward an upstream in the developer conveying direction on the developer bearing member.
In the immediately above developing device, because the developer container section is formed upstream of the second regulating member in the developer conveying direction, if the facing surface of the second regulating member is extended toward a downstream of the developer conveying direction, the capacity of the developer container section is reduced, thereby reducing the capacity to store the developer and as a result decreasing a developer life disadvantageously. Accordingly, the facing surface of the second regulating member is extended toward an upstream of the developer conveying direction, and thereby it is possible to have a greater volume of the developer container section and to elongate the developer life correspondingly in comparison with a case in which the second regulating member is extended downstream.
According to another preferred embodiment of the present invention, in the above developing device, a deviation of a magnetic force of the developer bearing member may be set within a range of giving no effect on the layer thickness of the developer passing through the second regulating member. Thereby, it is possible to prevent unevenness in taking toner into the developer caused by a deviation of the magnetic force of the developer bearing member in the axial direction of the developer bearing member.
According to still another preferred embodiment of the present invention, a developing apparatus includes a developer bearing member having a magnetic field generating device internally and configured to bear and convey two-component developer including toner and magnetic carrier, a first regulating member configured to regulate an amount of the developer born and conveyed by the developer bearing member, a developer container section for containing the developer scraped off by the first regulating member, a second regulating member arranged upstream of the first regulating member in a conveying direction of the developer on the developer bearing member, and a toner container section for supplying toner to the developer bearing member. The developing apparatus changes a toner take-in condition of the developer on the developer bearing member by changing a contact condition between the developer and the toner according to a change of a toner density of the developer on the developer bearing member. The second regulating member is spaced from the developer bearing member so as to regulate an increase of a layer thickness of the developer on the developer bearing member when the layer thickness thereof is increased due to a rise of the toner density of the developer. A surface of the second regulating member facing the developer bearing member is spaced from the surface of the developer bearing member such that a gap between an end portion of the facing surface of the second regulating member upstream in the developer conveying direction and the surface of the developer bearing member is larger than that between the downstream end portion of the facing surface of the second regulating member and the surface of the developer bearing member.
In the immediately above developing apparatus, the developer layer including the toner born by the developer bearing member is regulated by the second regulating member and the regulated developer forms a developer stagnated portion. The developer of the developer stagnated portion corresponding to the portion regulated by the facing surface of the second regulating member receives a reaction, which is a force acting in a direction against a conveyance of the developer applied, from the facing surface of the second regulating member. In addition, because the gap between the upstream end portion in the developer conveying direction of the facing surface of the second regulating member and the surface of the developer bearing member is larger than that between its downstream end portion and the surface of the developer bearing member, a component force in the same direction as for the normal component of a magnetic force generated by the magnetic field generating device is generated in the reaction from the facing surface. In other words, the developer in the developer stagnated portion corresponding to the portion regulated by the facing surface of the second regulating member receives the component force of the reaction applied by the facing surface of the second regulating member in addition to the magnetic force. This increases a frictional force on a contact interface between the developer stagnated portion and the developer layer born on the developer bearing member. Therefore, the toner in the developer is sufficiently charged, and thereby it is possible to prevent an occurrence of an uneven image density caused by insufficiently charged toner.
As a method of increasing a frictional force on the contact interface between the developer stagnated portion and the developer layer born on the developer bearing member, it is conceivable to increase the normal component of the magnetic force generated by the magnetic field generating device. However, increasing the normal component of the magnetic force may cause a self-regulating mechanism to not function appropriately for supplying toner in the developing apparatus.
More specifically, the developer stagnated portion formed by the developer regulated by the second regulating member becomes thicker as an increase of the developer passed through the first regulating member is regulated by the second regulating member. As the developer stagnated portion becomes thicker, the upper portion of the developer stagnated portion becomes further distant from the developer bearing member, and thereby it becomes hard for the developer to receive a conveying force of the developer bearing member. The developer finally reaches a saturated layer thickness where it is impossible to further increase the thickness. This saturated layer thickness is approximately proportional to a conveying force of the developer bearing member, in other words, the normal component of the magnetic force received by the developer. Therefore, the saturated layer thickness is increased as the normal component becomes greater.
In the above developing apparatus, however, an amount of supplied toner is automatically regulated at a constant level according to an increase and a decrease of a volume of the developer stagnated portion as described above, and therefore if the volume of the developer stagnated portion, i.e., the saturated layer thickness of the developer stagnated portion, is too large, a layer thickness of the developer stagnated portion fluctuates in a wide range. Such a wide range of the layer thickness fluctuation leads to an uneven toner take-in amount in the axial direction of the developer bearing member, thereby causing a toner density control to be harder or deteriorating a property of the developer stagnated portion to respond to supplying of toner. Thus, if the normal component of the above magnetic force is increased, the self-regulating mechanism for supplying toner may not function appropriately, resulting in an occurrence of a poor image.
Therefore, according to another preferred embodiment of the present invention, in the above developing apparatus, the normal component of the magnetic force, which is applied to the developer by the developer bearing member at the downstream end portion in the developer conveying direction on the surface of the second regulating member facing the developer bearing member, is set to be stronger than the normal component of the magnetic force applied to the developer by the developer bearing member at an upstream portion of the facing surface of the second regulating member in the developer conveying direction.
Accordingly, in the immediately above developing apparatus, because a force of the developer bearing member bearing and conveying developer is proportional to the normal component of the magnetic force applied to developer by the developer bearing member, the developer conveying force of the developer bearing member in the upstream becomes smaller than that in the downstream in the developer conveying direction, and thereby the saturated layer thickness of the developer stagnated portion formed in the upstream is decreased. Therefore, in the developer stagnated portion formed in the upstream, the layer thickness fluctuation becomes more sensitive to supplying of toner and the self-regulating mechanism for supplying toner functions appropriately, while in the downstream, the normal component of the magnetic force is set stronger than that in the upstream so as to achieve a sufficient frictional force on the contact interface between the developer stagnated portion and the developer layer born by the developer bearing member, thereby reliably preventing an insufficiently charged toner.
In the immediately above developing device, regarding the surface of the second regulating member facing the developer bearing member, if a gap between the end-most portion of the facing surface of the second regulating member upstream in the developer conveying direction and the developer bearing member is smaller than the layer thickness of the developer on the developer bearing member, the developer on the developer bearing member is also regulated by a substrate portion of the second regulating member. The developer regulated by the substrate portion of the second regulating member does not receive the component force of the reaction applied by the facing surface of the second regulating member as described above, and therefore the developer stagnated portion is easily diffused and there is a possibility that the developer overflows into the toner container section.
Accordingly, according to still another preferred embodiment of the present invention, in the immediately above developing apparatus, regarding the surface of the second regulating member facing the developer bearing member, the gap between the end-most portion of the surface of the second regulating member upstream in the developer conveying direction and the developer bearing member is set to be larger than the layer thickness of the developer on the developer bearing member. Therefore, the developer layer on the developer bearing member can be regulated only by the facing surface of the second regulating member, and accordingly, diffusion of the developer stagnated portion can be suppressed so as to prevent the developer from overflowing into the toner container portion.
According to still another preferred embodiment of the present invention, a developing apparatus includes a developer bearing member having a magnetic field generating device internally and configured to bear and convey two-component developer including toner and magnetic carrier, a first regulating member configured to regulate an amount of the developer born and conveyed by the developer bearing member, a developer container section for containing the developer scraped off by the first regulating member, and a toner container section for supplying toner to the developer bearing member. The developer container section has a second regulating member arranged upstream of the first regulating member in a conveying direction of the developer on the developer bearing member and the second regulating member is spaced from the developer bearing member so as to regulate an increase of a layer thickness of the developer on the developer bearing member when the layer thickness of the developer is increased due to a rise of a toner density of the developer. Further, a developer circulating portion is formed for circulating the developer obstructed by the second regulating member, and also, a developer stagnated portion, where the developer stands still when a toner density of the developer is within a predetermined appropriate range, is formed in a toner supplying path connecting the toner container section with the developer circulating portion, such that a contact condition between the developer and the toner is changed according to a change of the toner density of the developer on the developer bearing member and thereby a condition of taking the toner into the developer is changed. Furthermore, the second regulating member is configured so as to suppress the diffusion of the developer circulating portion.
In the immediately above developing apparatus, the developer obstructed by the second regulating member moves upstream in the developer conveying direction of the second regulating member to form the developer circulating portion where the developer circulates. When the toner density of the developer is within a predetermined appropriate range, a developer stagnated portion where the developer stands still is formed in the toner supplying path connecting the developer circulating portion with the toner container section so as to prevent the toner from being taken into the developer at a contact portion between the toner and the developer. When the toner density of the developer is decreased, the developer in the developer stagnated portion is taken into the developer circulating portion and thereby the developer stagnated portion disappears, by which the developer is put in contact with the toner in the toner supplying path and the developer is mixed with the toner by agitation in the developer circulating portion. In this condition, diffusion of the developer circulating portion is suppressed by the second regulating member, and therefore the developer circulating portion does not extend toward the toner container section in the toner supplying path. Accordingly, the developer in the developer circulating portion does not diffuse and overflow into the toner container section. Thus, in the developing apparatus of the present invention, it is possible to change the contact condition between the developer and the toner according to the toner density of the developer to change the toner take-in condition of the developer without any partition between the toner supplying path and the toner container section, and further possible to prevent the developer in the developer circulating portion from overflowing into the toner container section. Further, unlike the case of arranging a partition, a bridge of developer will not be formed by the stagnated developer on the wall surfaces of the developer stagnated portion in the toner supplying path, and therefore toner replenishment from the toner container section will not be stopped by such a developer bridge. As a result, the toner density can be stabilized.
According to another embodiment of the present invention, in the immediately above developing apparatus, the second regulating member includes a developer layer thickness regulating section, which is spaced from the developer bearing member so as to regulate an increase of a layer thickness of the developer on the developer bearing member when the layer thickness of the developer is increased due to a rise of a toner density of the developer, and a circulating direction regulating section for regulating the motion of the developer so that the developer circulating section does not diffuse toward the toner container section when the developer obstructed by the developer layer thickness regulating section moves toward upstream in the developer conveying direction to form the developer circulating portion. Thus, because the developer circulating section regulates a moving direction of the developer obstructed by the developer layer thickness regulating section of the second regulating member toward upstream in the developer conveying direction so that the developer circulating portion does not diffuse to the toner container section, the developer circulating portion does not extend toward the toner container section and thereby the developer is prevented from overflowing into the toner container section.
Further, according to another embodiment of the present invention, in the immediately above developing apparatus, the circulating direction regulating section of the second regulating member is a surface facing the developer bearing member extending from the developer layer thickness regulating section toward the upstream in the developer conveying direction. When the developer obstructed by the developer layer thickness regulating section of the second regulating member moves toward the upstream of the developer layer thickness regulating section in the developer conveying direction, the developer moves along the surface of the second regulating member facing the developer bearing member extending from the developer layer thickness regulating section toward the upstream in the developer conveying direction. The developer then diffuses to the toner container section and is obstructed. In this manner, the surface of the second regulating member facing the developer bearing member extending from the developer layer thickness regulating section toward the upstream in the developer conveying direction regulates the developer moving direction toward upstream in the developer conveying direction to such a direction that the developer circulating portion does not diffuse to the toner container section.
According to still another embodiment of the present invention, the surface facing the developer bearing member of the second regulating member may be non-magnetic. In the above developing apparatus, if the facing surface of the second regulating member is magnetic, a bridge of developer is formed between the surface of the second regulating member facing the developer bearing member and the developer bearing member. When the toner density is decreased in the developer on the developer bearing member due to a toner consumption, a force of obstructing taking toner into the developer is increased by the bridge of the developer formed between the facing surface of the second regulating member and the developer bearing member, by which it may be caused that a required amount of toner will not be taken into the developer. If the above-described phenomenon is repeated, an abnormal image having, for example, blank areas may occur. Therefore, a non-magnetic material is used for the surface of the second regulating member facing the developer bearing member, thereby preventing a developer bridge from being formed between the facing surface of the second regulating member and the developer bearing member. Thereby, even when the toner density of the developer is decreased, a required amount of toner can be taken into the developer.
According to still another preferred embodiment of the present invention, a developing apparatus includes a developer bearing member having a magnetic field generating device internally and configured to bear and convey two-component developer including toner and magnetic carrier, a first regulating member configured to regulate an amount of the developer born and conveyed by the developer bearing member, a developer container section for containing the developer scraped off by the first regulating member, and a toner container section provided adjacent to the developer container section for supplying toner to the developer bearing member. The developer container section has a second regulating member arranged upstream of the first regulating member in the conveying direction of the developer on the developer bearing member, and the second regulating member is spaced from the developer bearing member so as to regulate an increase of a layer thickness of the developer when the layer thickness of the developer is increased due to a rise of a toner density of the developer. Further, a developer circulating portion is formed for circulating the developer obstructed by the second regulating member, and also, a developer stagnated portion, where the developer stands still when a toner density of the developer is within a predetermined appropriate range, is formed in a toner supplying path connecting the toner container section with the developer circulating portion, such that a contact condition between the developer and the toner is changed according to a change of the toner density of the developer on the developer bearing member and thereby a condition of taking toner into the developer is changed. Furthermore, a developing apparatus frame is configured so as not to disturb an ear crack portion of the developer, which is formed on the developer bearing member by a magnetic pole opposite to the developer circulating portion. Because the developing apparatus frame does not disturb an ear crack portion of the developer which is formed on the developer bearing member by a magnetic pole opposite to the developer circulating portion, the ear crack portion of the developer can stably be in contact with the developer circulating portion. Further, due to such a stable ear crack portion, toner in the developer circulating portion is actively taken into the developer on the developer bearing member. Therefore, the toner density is stabilized and an even image can be obtained even when a halftone image is formed.